I. Field
The present disclosure relates generally to communication, and more specifically to rate control for a communication system.
II. Background
In a wireless communication system, a transmitting station processes traffic data for one or more data streams, generates one or more modulated signals, and transmits the modulated signal(s) via a wireless channel to a receiving station. The modulated signal(s) may experience various deleterious channel conditions such as, e.g., fading, multipath, and interference effects. The receiving station receives the modulated signal(s) and processes one or more received signals to recover the traffic data.
Rate control refers to the process for controlling the rate for each data stream sent by the transmitting station to the receiving station. A “rate” may be associated with a particular data rate, a particular coding scheme or code rate, a particular modulation scheme, and so on to use for a data stream. Rate control attempts to select a rate that is as high as possible while meeting a target packet error rate (PER) for each data stream based on the channel conditions such that the data stream can be reliably received.
Rate control is often performed in a closed-loop manner. For closed-loop rate control, the transmitting station typically transmits a pilot that is used by the receiving station to estimate the channel quality, which may be quantified by a signal-to-noise-and-interference ratio (SNR). The receiving station then selects one or more rates based on the estimated channel quality and sends the selected rate(s) back to the transmitting station. The transmitting station processes the traffic data based on the selected rate(s).
Closed-loop rate control is generally effective but may not always be available. Furthermore, there are some disadvantages with closed-loop rate control. First, the transmitting station expends system resources to transmit the pilot to the receiving station, and the receiving station expends system resources to send back the selected rate(s). Second, additional delays are typically incurred for the transmitting station to transmit the pilot and for the receiving station to send back the selected rate(s).
There is therefore a need in the art for techniques to perform rate control when closed-loop rate control is not available or when good performance using less system resources, e.g. transmission overhead to communicate channel quality, and with less delay is desired.